Monitoring of the operation of a subscriber unit

ABSTRACT

In a method of monitoring the operation of a subscriber unit in a telecommunication system, in order to detect possible malfunctions as early as possible, a call reserved in signaling for some other purpose is transmitted to the subscriber unit, whereupon a call to which the subscriber unit automatically responds is selected as the call. A message about receiving the call is awaited from the subscriber unit, and, if not such message is received from the subscriber unit, the call is repeated until the subscriber unit has left a predetermined number of transmitted calls unanswered, whereupon an alarm is given.

BACKGROUND OF THE INVENTION

The invention relates to a method of monitoring the operation of asubscriber unit of a telecommunication system. The invention alsorelates to a subscriber network element of a radio system providing awireless local loop, the subscriber network element having a datatransmission connection with a telephone exchange and comprising meansfor establishing, via base stations, a radio connection to thesubscriber units located in the coverage area of the radio system, fortransmitting telecommunication signals between the subscriber units andthe exchange.

The invention relates in particular to monitoring the operation of asubscriber unit to be used in a WLL system, i.e. a radio systemproviding a wireless local loop. In a WLL system, an ordinary two-wiretelephone set is connected via a radio connection by means of a specialterminal equipment to the local exchange, which in turn is connected tothe public telephone network via network cabling. In this connection, asubscriber unit refers to the equipment the subscriber has fortransmitting and receiving telecommunication signals, i.e. in case ofthe WLL system, the subscriber unit comprises a WLL terminal equipmentconsisting of a radio part and a teleadapter (to which the userinterface, e.g. a telephone, is connected), and a user interface, suchas a telephone, a telefax terminal, a computer/modem combination or thelike, connected to the terminal equipment.

To guarantee the interference-free transfer of telecommunicationsignals, for example phone calls, it is necessary to monitor subscriberunits so that possible malfunctions will be detected as early aspossible. It is especially important to monitor WLL subscriber units,since they are more prone to malfunctions than normal subscriber unitsoperating via a cable.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a method of monitoring theoperation of subscriber units so that possible malfunctions will bedetected as early as possible, even before the user of the subscriberunit notices that a malfunction has occurred. These aims are achievedwith the method according to the invention, which is characterized inthat a call reserved in signalling for some other purpose is transmittedto the subscriber unit, a call to which the subscriber unitautomatically responds being selected as the call, a message is awaitedfrom the subscriber unit about receiving the call, and if the message isnot received from the subscriber unit, the call is repeated until thesubscriber unit has left a predetermined number of transmitted callsunanswered, whereupon an alarm is given.

The invention is based on the idea that malfunctions in a subscriberunit can be detected very early, when the operation of the subscriberunit is systematically tested during light traffic by transmitting acall to the subscriber unit and by receiving a message from thesubscriber unit about receiving the call, when the subscriber unit isout of use, i.e. when the user of the unit is not using his or her unit.Since a call which already exists for some other purpose and to whichthe subscriber unit automatically responds is chosen as the test call,there is no need to define for the subscriber unit a special call forthe test. If the subscriber unit responds to the transmitted call, it isconsidered to be in order. Otherwise the call is repeated at certainintervals as many times as the operator has determined, after which thesubscriber unit is considered to be faulty, unless it has by thentransmitted a message about receiving the call. The most importantadvantage of the method according to the invention is that the operationof the subscriber unit can be monitored continuously, i.e. also when theunit is not used for a long time, without having to define a specialtest call for the subscriber unit for this purpose. The method accordingto the invention can thus be applied to all existing units withouthaving to specifically design a subscriber unit to make the testingpossible.

In one preferred embodiment of the method according to the invention,the connection to the subscriber unit is released as soon as a messagehas been received from the subscriber unit about receiving the call,i.e. before the subscriber unit forwards the call to the user of theunit. Thus the operation of the subscriber unit can be monitoredcompletely automatically without the user of the unit having toparticipate in any way in the monitoring or even having to know aboutthe test.

The invention also relates to a subscriber network element by means ofwhich the method of the invention can be applied. The subscriber networkelement according to the invention is characterized in that thesubscriber network element comprises testing means for monitoring theoperation of the subscriber unit, the testing means comprising atransmitting unit for transmitting a call reserved in signalling forsome other purpose to the subscriber unit, the call being of the type towhich the subscriber unit automatically responds, a receiving unit forreceiving a message transmitted by the subscriber unit as a response tothe call, and a control unit, which causes the transmitting unit totransmit the call again until the receiving unit has received themessage, or until the call has been transmitted a predetermined numberof times, whereupon the control unit gives an alarm.

BRIEF DESCRIPTION OF THE DRAWING

In the following, the invention will be described in greater detail bymeans of its first preferred embodiment with reference to theaccompanying which

FIG. 1 is a block diagram of a part of a WLL system, and

FIG. 2 is a partial block diagram of the subscriber network elementshown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a part of a WLL system where the methodaccording to the invention can be applied. The subscriber unit 1 shownin the figure comprises a user interface, i.e. a telephone 2, and aterminal equipment 3. The phone in FIG. 1 is an ordinary phone connectedto the exchange by means of a two-wire line. Instead of the phone 2, thesystem shown in the figure could equally well employ some other ordinaryuser interface, such as a telefax terminal or a computer/modemcombination, connected to the exchange by means of a two-wire lead.

The phone 2 and the terminal equipment 3 are connected in FIG. 1 by atwo-wire lead 4, through which telecommunication signals can betransmitted between the terminal equipment and the phone. The terminalequipment 3 comprises signal processing means for adapting a speech pathto a radio channel. Such signal processing means are for example a radiopart consisting of an antenna 8, a radio transmitter and a radioreceiver, and a teleadapter which adapts the radio part to an ordinarytelephone set 2.

The subscriber unit 1 is connected via the antenna 8 to a base station 5(FIG. 1 shows three base stations BS) through which the calls aretransmitted, via a subscriber network element 6, to the PSTN (PublicSwitched Telephone Network), i.e. the fixed telephone network 7. Thesubscriber network element 6 thus comprises a base station controllerfor controlling the base stations 5, and means for maintaining thetelecommunication connection to the fixed phone network.

The base stations 5 correspond to the base stations of an NMT-450icellular radio system (Nordisk Mobil Telefon). Thus, as far as thesignal transmission is concerned, the subscriber unit 1 functions like anormal hand-held mobile phone of the NMT-450i system. Through the basestations 5 and the subscriber network element 6, calls can also be madewith an ordinary mobile phone of the NMT-450i system, provided that thenetwork operator has programmed the subscriber network element with aview to connecting calls for such a phone. In such a case, theaforementioned NMT phone can only be used, however, in the coverage areaof one base station 5, since the network element shown in the figuredoes not include handover means with which an on-going call could betransferred between the base stations.

FIG. 2 represents a partial block diagram of the subscriber networkelement of FIG. 1. FIG. 2 shows only the testing means which are neededfor monitoring the operation of subscriber units during light traffic.The aforementioned testing is preferably carried out at least partiallyby means of a computer program. At a time of the day determined by thenetwork operator, a transmitting unit 9 included in the testing meanstransmits a test call alternately to each of the subscriber units in thesubscriber unit register of the subscriber network element. The testcall to be transmitted is the same as the message for an ending callused in the NMT-450i system. When the terminal equipment of thesubscriber unit detects the call, it responds to it by transmitting apredetermined message to the subscriber network element 6. A receivingunit 10 in the subscriber network element detects the aforementionedmessage and forwards it to a control unit 11. Since in the exemplarycase the test call is the same as the message for an ending call, theterminal equipment 3 of the subscriber unit 1 does not forward thereceived message to the phone 2. The user of the subscriber unit doesnot thus detect the test at all.

If the subscriber unit 1 does not respond to the call, i.e. the controlunit 11 does not receive a message from the subscriber unit through thereceiving unit 10, the control unit 11 marks down that particularsubscriber unit to a special list of subscriber units to be monitoredand causes the transmitting unit 9 to repeat the call again after acertain delay. If the subscriber unit 1 still does not respond to thecall, the control unit 11 causes the transmitting unit 9 to repeat thecall a third time (the number of the repeated calls is determined by thenetwork operator), before it considers the subscriber unit to be faultyand gives an alarm by transmitting a message to the network operator orby marking down the code of the faulty unit to a special register.

If the subscriber unit to be tested is engaged when the test begins, thesubscriber network element 6 immediately discontinues the test withoutsending a test call and interprets that the subscriber unit is in order.

It must be understood that even if the invention is described above, byway of example, only in connection with the WLL system, the methodaccording to the invention can also be applied in the subscriber unitsof other systems. Thus, the method according to the invention canequally well be used to monitor the operation of subscriber units of,for example, a cellular radio system or a fixed, i.e. wired,telecommunication system. The preferred embodiments of the method andthe subscriber network element according to the invention may thus varywithin the scope of the appended claims.

We claim:
 1. A method of monitoring the operation of a subscriber unitof a telecommunication system having provisions which reserve insignaling a given call for a purpose other than monitoring operation ofa subscriber unit, and to which the subscriber unit, upon receiving thegiven call, automatically, said method comprising the stepsof:transmitting the given call to the subscriber unit; awaiting receiptof a message from the subscriber unit about receiving the given call;and if the message is not received from the subscriber unit, repeatingtransmitting of the given call until the subscriber unit has left apredetermined number of transmitted instances of the given callunresponded to, and thereupon giving an alarm, wherein a message for anending call is used as the given call.
 2. The method according to claim1, further comprising:if a message is received from the subscriber unitabout receiving the given call, releasing a respective connection suchas to prevent the subscriber unit from forwarding the given call it hasreceived, to a user of the subscriber unit.
 3. The method according toclaim 2, wherein:said transmitting is accomplished by transmitting thegiven call by radio-frequency signals to the subscriber unit, and saidresponding is accomplished by the subscriber unit transmittingradio-frequency signals.
 4. The method according to claim 3, wherein:thesubscriber unit is a subscriber unit of a radio system providing awireless local loop.
 5. The method according to claim 1 or 2,wherein:said transmitting is accomplished by transmitting the given callduring light traffic on a normal calling channel of the subscriber unit.6. A subscriber network element of a radio system providing a wirelesslocal loop, said subscriber network element having a data transmissionconnection with a telephone exchange, said subscriber networkcomprising:means for establishing, via a base system, a radio connectionto a subscriber unit located in a coverage area of the radio system, fortransmitting telecommunication signals between the subscriber unit andthe exchange; and testing means for monitoring operation of thesubscriber unit, said testing means comprising:a transmitting unit fortransmitting a given call which already is reserved in signaling in thebase system for some other purpose, to the subscriber unit, the givencall being of a type to which the subscriber unit upon receiving thegiven call automatically responds by sending a given message, areceiving unit for receiving the given message, if transmitted by thesubscriber unit, as a response to the given call, and a control unitwhich causes the transmitting unit to transmit the given call again, ifno given message is received, until the receiving unit has received themessage and sent a given message, or until the given call has beentransmitted a predetermined number of times by the transmitting unit,whereupon the control unit gives an alarm, wherein the transmitting unitis arranged to use a message for an ending phone call as the given call.7. The subscriber network element according to claim 6, furthercomprising:a timing device and a subscriber unit register listing thesubscriber unit; the testing means being arranged to test the subscriberlisted in the subscriber register, at a time indicated by the timingdevice.